Lithium ion battery and method for manufacturing the same

ABSTRACT

A lithium ion secondary battery is disclosed that can inhibit generation of gas due to decomposition of a non-aqueous electrolyte solution. The lithium ion battery includes a cathode, a non-aqueous electrolyte solution and an anode, wherein the cathode includes a conductive material, a layered niobium-containing oxide that coats a surface of the conductive material, and a lithium-containing oxide active material having an upper-limit potential to a redox potential of metal lithium of no less than 4.5 V (vs. Li/Li + ).

This application claims priority to Japanese Application No. 2016-058934filed Mar. 23, 2016, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to lithium ion batteries and methods formanufacturing the same.

BACKGROUND

Patent Literature 1 discloses a non-aqueous electrolyte solution lithiumion battery including LiNi_(0.5)Mn_(1.5)O₄ as a cathode active material.LiNi_(0.5)Mn_(1.5)O₄ has an upper-limit potential to the redox potentialof metal lithium of no less than 4.5 V (vs. Li/Li⁺), which is a highpotential. By using such a high potential cathode active material, it ispossible to easily increase the operating voltage of a lithium ionbattery. However, if a high potential cathode active material is used, aproblem arises that gases are generated in the battery due todecomposition of the non-aqueous electrolyte solution.

In order to solve this problem, various improvements are proposed to thecathodes of lithium ion batteries. For example, Patent Literatures 2 to4 suggest coating the surface of a cathode active material with aniobium-containing oxide and the like. Patent Literature 5 suggestsmixing a niobium-containing oxide in a cathode mixture that forms acathode. According to the techniques disclosed in Patent Literatures 2to 5, it is considered that the area where the cathode active materialand the non-aqueous electrolyte solution directly contact with eachother can be reduced by the niobium-containing oxide and the like,whereby the reaction of the cathode active material and the non-aqueouselectrolyte solution can be inhibited and the decomposition of thenon-aqueous electrolyte solution can be inhibited. It is also consideredthat the niobium-containing oxide functions as a negative catalyst inthe cathode mixture, whereby the activity of the cathode active materiallowers and the decomposition of the non-aqueous electrolyte solution canbe inhibited.

CITATION LIST Patent Literatures

Patent Literature 1: JP 2012-124026 A

Patent Literature 2: JP 2015-144108 A

Patent Literature 3: JP 2015-204256 A

Patent Literature 4: JP 2011-070789 A

Patent Literature 5: JP 2004-319268 A

SUMMARY OF THE DISCLOSURE Technical Problem

Patent Literatures 2 to 5 each discloses a technique of inhibiting thereaction of a cathode active material and a non-aqueous electrolytesolution. However, the inventors of the present disclosure have newlyfound that the decomposition of a non-aqueous electrolyte solution in ahigh-voltage lithium battery is not only due to the reaction with acathode active material. That is, in order to further inhibit thegeneration of gas due to decomposition of the non-aqueous electrolytesolution, they considered that a method other than the methods of“coating the surface of the cathode active material” and “mixing anegative catalyst in the cathode mixture” as disclosed in PatentLiteratures 2 to 5 is needed.

Considering the above, disclosed is a lithium ion secondary battery thatcan inhibit generation of gas due to decomposition of a non-aqueouselectrolyte solution, and a method for manufacturing the lithium ionsecondary battery.

Solution to the Problem

The inventors presumed that, in a lithium ion battery including a highpotential cathode active material, gases are generated due todecomposition of a non-aqueous electrolyte solution, with the followingmechanisms.

(1) In a cathode mixture, there is a conductive material that contactsthe cathode active material.(2) When the cathode active material has a high potential, theconductive material that contacts the cathode active material also has ahigh potential.(3) When the conductive material having a high potential and thenon-aqueous electrolyte solution contact each other, the non-aqueouselectrolyte solution decomposes on the surface of the conductivematerial, whereby gases are generated.

The above presumed mechanisms had not been considered at all before. Asa result of various research based on the presumed mechanisms, theinventors of the present disclosure found that the generation of gas canbe remarkably inhibited by coating the surface of the conductivematerial with a niobium-containing oxide.

Based on the above findings, the present disclosure is directed to thefollowing embodiments. That is, an embodiment of the present disclosureis a lithium ion battery including: a cathode; a non-aqueous electrolytesolution; and an anode, wherein the cathode includes a conductivematerial, a layered niobium-containing oxide that coats a surface of theconductive material, and a lithium-containing oxide active materialhaving an upper-limit potential to a redox potential of metal lithium ofno less than 4.5 V (vs. Li/Li⁺).

“Layered niobium-containing oxide that coats a surface of the conductivematerial” means that the surface of the conductive material iscontinuously coated with the niobium-containing oxide along the surfaceshape of the conductive material. That is, it means that the surface ofthe conductive material is coated with a film of the niobium-containingoxide, or that the niobium-containing oxide is accumulated in a layer onthe surface of the conductive material. It is noted that theniobium-containing oxide does not have to cover the whole surface of theconductive material, and it may be a layer(s) including a discontinuouspart. In this point, the lithium ion battery of the present disclosureis clearly different from the conventional batteries (batteries in whichsurfaces of active materials are coated, or batteries in whichconductive materials and niobium-containing oxides are simply mixed).

“Niobium-containing oxide” means that niobium is contained as an elementconstituting the oxide. The niobium-containing oxide may include, inaddition to niobium and oxygen, elements other than niobium and oxygen.

“Lithium-containing oxide active material having an upper-limitpotential to a redox potential of metal lithium of no less than 4.5 V(vs. Li/Li⁺)” means that part of the potential of the lithium-containingoxide active material at which lithium is occluded/released is no lessthan 4.5 V to the redox potential of metal lithium. That is, thelithium-containing oxide active material is a cathode active material ofa lithium ion battery, and has a flat part at a potential of no lessthan 4.5 V (vs. Li/Li⁺).

“Lithium-containing oxide” means that lithium is contained as an elementconstituting the oxide. “Lithium-containing oxide” is not particularlylimited in the constituent elements other than lithium and oxygen andcomposition ratio of the elements, as long as the lithium-containingoxide is an active material that has an upper-limit potential to theredox potential of metal lithium of no less than 4.5 V (vs. Li/Li⁺).

In the lithium ion battery of the present disclosure, the thickness ofthe layered niobium-containing oxide may be no less than 0.4 nm.

In the lithium ion battery of the present disclosure, the thickness ofthe layered niobium-containing oxide may be in the range of from 0.4 nmto 5 nm.

In the lithium ion battery of the present disclosure, the conductivematerial may be formed from a carbon material.

An embodiment of the present disclosure is a method for manufacturing alithium ion battery including: coating a surface of a conductivematerial with a layered niobium-containing oxide to form a complex;mixing the complex and a lithium-containing oxide active material havingan upper-limit potential to a redox potential of metal lithium of noless than 4.5 V (vs. Li/Li⁺) to obtain a cathode mixture; manufacturinga cathode from the cathode mixture; and manufacturing a power generationelement from the cathode, a non-aqueous electrolyte solution and ananode.

In the manufacturing method of the present disclosure, in the coating,the surface of the conductive material may be coated with the layeredniobium-containing oxide by an atomic layer deposition (ALD).

According to the lithium ion battery of the present disclosure, it ispossible to inhibit generation of gas due to decomposition of thenon-aqueous electrolyte solution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view to explain the structure of a lithium ionbattery 100;

FIG. 2 is a flow chart to explain a method for manufacturing a lithiumion battery (S100);

FIGS. 3A and 3B include a HAADF-STEM image of the surface of a complex(conductive material and layered niobium-containing oxide) used inExample 3; and

FIGS. 4A and 4B include a HAADF-STEM image and a view to show theresults of elemental analysis of the surface of the complex (conductivematerial and layered niobium-containing oxide) used in Example 3.

In the drawings, the reference numbers are used throughout to refer tothe same elements. The various features, advantages and technicalaspects of the embodiments of the disclosure will be described below.

DESCRIPTION OF EMBODIMENTS 1. Lithium Ion Battery 100

A lithium ion battery 100 in FIG. 1 includes a cathode 10, a non-aqueouselectrolyte solution 20 and an anode 30. The cathode 10 includes aconductive material 11 a, a layered niobium-containing oxide 11 bcoating on the surface of the conductive material 11 a, and alithium-containing oxide active material 12 having an upper potential tothe redox potential of metal lithium of no less than 4.5 V (vs. Li/Li⁺).

1.1. Cathode 10 1.1.1. Conductive Material 11 a

The cathode 10 includes the conductive material 11 a. Examples of theconductive material 11 a include conductive materials formed from acarbon material such as vapor-grown carbon fiber, acetylene black (AB),Ketjen black (KB), carbon nanotube (CNT) and carbon nanofiber (CNF), andconductive materials formed from a metal material that can endure theuse environment of non-aqueous electrolyte solution lithium ionbatteries. Specifically, a conductive material formed from a carbonmaterial may be used. For the conductive material 11 a, one kind may beused alone, or a mixture of two or more kinds may also be used.

The conductive material 11 a may be particulate or fibrous. If theconductive material 11 a is formed as particles, the primary particlediameter may be in the range of from 5 nm to 100 nm, and the aspectratio may be less than 2. The lower limit of the primary particlediameter of the particulate conductive material 11 a may be no less than10 nm, and may be no less than 15 nm. The upper limit may be no morethan 80 nm, and may be no more than 65 nm. By using such a particulateconductive material 11 a, it is possible to further improve theconductivity of the cathode 10. If the conductive material 11 a isformed as fibers, the fiber diameter thereof may be in the range of from10 nm to 1 μm, and the aspect ratio may be no less than 20. The lowerlimit of the fiber diameter of the fibrous conductive material 11 a maybe no less than 30 nm, and may be no less than 50 nm. The upper limitmay be no more than 700 nm, and may be no more than 500 nm. The lowerlimit of the aspect ratio of the fibrous conductive material may be noless than 30, and may be no less than 50.

The content of the conductive material 11 a in the cathode 10 is notparticularly limited. For example, setting the total amount of theconductive material 11 a, and the lithium-containing oxide activematerial 12 and the binder 13, which are described later, as 100 mass %,the content of the conductive material 11 a may be no less than 2 mass%, may be no less than 5 mass %, and may be no less than 7 mass %. Theupper limit is not particularly limited, and may be no more than 15 mass%, may be no more than 13 mass %, and may be no more than 10 mass %.With the content of the conductive material 11 a in these ranges, it ispossible to obtain the cathode 10 with excellent ion conductivity andelectron conductivity.

1.1.2. Layered Niobium-Containing Oxide 11 b

The cathode 10 includes the layered niobium-containing oxide 11 b thatcoats the surface of the conductive material 11 a. For example, as shownin FIG. 1, the cathode 10 includes the niobium-containing oxide 11 bcontinuously coating the surface of the conductive material 11 a in amanner to be along the surface shape of the conductive material 11 a. Inother words, a film of the niobium-containing oxide 11 b coats thesurface of the conductive material 11 a. Alternatively, theniobium-containing oxide 11 b in layer is accumulated on the surface ofthe conductive material 11 a. In this way, the cathode 10 includes acomplex 11 of the conductive material 11 a and the niobium-containingoxide 11 b.

The complex 11 shown in FIG. 1 may be considered as a core-shellstructure in which the conductive material 11 a is a core and theniobium-containing oxide 11 b is a shell. However, in the complex 11,the niobium-containing oxide 11 b does not have to cover the wholesurface of the conductive material 11 a, and may be a layer(s) includinga discontinuous part. In other words, in the complex 11, part of thesurface of the conductive material 11 a may be exposed. In this case, noless than 50% of the surface of the conductive material 11 a may becoated with the niobium-containing oxide 11 b. The coated part may be noless than 70%, and may be no less than 90%.

“Niobium-containing oxide” is an oxide including niobium as aconstituent element. “Niobium-containing oxide” may include an elementother than niobium and oxygen, in addition to niobium and oxygen. Forexample, as the element other than niobium and oxygen, one or moreelements selected from the group consisting of lithium, carbon andnitrogen may be included.

Specific examples of “niobium-containing oxide” include niobium oxideand lithium niobate. These oxides can further inhibit generation of gasdue to decomposition of the non-aqueous electrolyte solution.

The layered niobium-containing oxide 11 b may have a thickness of noless than 0.4 nm. This is because generation of gas due to decompositionof the non-aqueous solution may be further inhibited with thisthickness. The upper limit of the thickness is not particularly limited,and with any thickness, generation of gas due to decomposition of thenon-aqueous electrolyte solution may be inhibited. However, according tothe findings of the inventors of the present disclosure, in addition tothe effect of inhibiting generation of gas due to decomposition of thenon-aqueous electrolyte solution, a new effect of making the resistanceof the cathode 10 small is obtained, by making the thickness of thelayered niobium-containing oxide 11 b no more than 5 nm. That is, thelayered niobium-containing oxide 11 b especially may have a thickness inthe range of from 0.4 nm to 5 nm.

Whether the surface of the conductive material 11 a is coated with thelayered niobium-containing oxide 11 b or not can be easily confirmed forexample by obtaining a HAADF-STEM image by a high-angle annulardark-field method by means of a scanning transmission electronmicroscope (HAADF-STEM method).

1.1.3. Lithium-Containing Oxide Active Material 12

The cathode 10 includes the lithium-containing oxide active material 12having an upper potential to the redox potential of metal lithium of noless than 4.5 V (vs. Li/Li⁺). Part of the potential of thelithium-containing oxide active material 12 at which lithium isoccluded/released is no less than 4.5 V to the redox potential of metallithium. That is, the lithium-containing oxide active material 12 is acathode active material of the lithium ion battery 100, and has a flatpart at a potential of no less than 4.5 V (vs. Li/Li⁺). For thelithium-containing oxide active material 12, one kind may be used alone,or a mixture of two or more kinds may also be used.

“Lithium-containing oxide” means that lithium is contained as an elementthat constitutes the oxide. The kind of the “lithium-containing oxide”is not particularly limited as long as the oxide is an active materialhaving an upper potential to the redox potential of metal lithium of noless than 4.5 V (vs. Li/Li⁺). For example, by including one or moreelements selected from nickel, manganese and cobalt in thelithium-containing oxide as an element other than lithium and oxygen, itis possible to form the active material 12 of such a high potential.

Specific examples of “lithium-containing oxide” include lithium nickelmanganese composite oxides of a spinel structure, lithium nickel cobaltmanganese oxide of a layered structure, and cobalt olivine of an olivinestructure. Specifically, lithium nickel manganese composite oxides of aspinel structure may be used, because a cathode active material of muchhigher potential may be made.

The shape of the lithium-containing oxide active material 12 is notparticularly limited. For example, it may be formed as particles or athin film. If the lithium-containing oxide active material 12 is formedas particles, the primary particle diameter may be in the range of from1 nm to 100 μm. The lower limit may be no less than 10 nm, may be noless than 100 nm, and may be no less than 500 nm. The upper limit may beno more than 30 μm, and may be no more than 10 μm. Thelithium-containing oxide active material 12 may form a secondaryparticle in which the primary particles are gathered or agglomerated. Inthis case, the particle diameter of the secondary particle is notparticularly limited, and normally in the range of from 3 μm to 50 μm.The lower limit may be no less than 4 μm, and the upper limit may be nomore than 20 μm. The cathode 10 having excellent ion conductivity andelectron conductivity may be obtained with the lithium-containing oxideactive material 12 having such a range of particle diameter.

The content of the lithium-containing oxide active material 12 in thecathode 10 is not particularly limited. For example, setting the totalamount of the above-mentioned conductive material 11 a and thelithium-containing oxide active material 12, and the binder 13 which isdescribed later as 100 mass %, the content of the lithium-containingoxide active material 12 may be no less than 80 mass %, may be no lessthan 85 mass %, and may be no less than 90 mass %. The upper limit isnot particularly limited, and may be no more than 98 mass %, may be nomore than 97 mass %, and may be no more than 95 mass %. With the contentof the lithium-containing oxide active material 12 in these ranges, itis possible to obtain the cathode 10 having excellent ion conductivityand electron conductivity.

The cathode 10 may include a cathode active material other than thelithium-containing oxide active material 12 in a part. For example, thecathode 10 may include a cathode active material having an upperpotential to the redox potential of metal lithium of less than 4.5 V(vs. Li/Li⁺). However, in view of easily increasing the operatingvoltage of the lithium ion battery, no less than 80 mass % of thecathode active material included in the cathode 10 may be thelithium-containing oxide active material 12.

1.1.4. Binder 13

The cathode 10 optionally includes the binder 13. For the binder 13, anybinder used for lithium ion batteries may be applied. Examples thereofinclude styrene butadiene rubber (SBR), carboxymethylcellulose (CMC),acrylonitrilebutadiene rubber (ABR), butadiene rubber (BR),polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). Forthe binder 13, one kind may be used alone, or a mixture of two or morekinds may also be used. The content of the binder 13 in the cathode 10is not particularly limited, and for example the same amount as thebinder included in the cathode of a conventional lithium ion battery maybe contained.

The cathode 10 includes a cathode mixture layer 14 that includes theabove-described conductive material 11 a, layered niobium-containingoxide 11 b and lithium-containing oxide active material 12. Thethickness of the cathode mixture layer 14 is not particularly limited,and for example may be in the range of from 0.1 μm to 1 mm, and may bein the range of from 1 μm to 100 μm.

1.1.5. Cathode Current Collector 15

The above-described cathode mixture layer 14 is connected to a cathodecurrent collector 15, which makes it possible to take out the electricalenergy from the cathode current collector 15, via terminals and the like(not shown). The cathode current collector 15 is formed, for example,from a metal material including one or two or more elements selectedfrom the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr,Zn, Ge and In. The shape of the cathode current collector 15 is notparticularly limited, and may be in the form of a foil, mesh, or othervarious shapes.

1.2. Non-Aqueous Electrolyte Solution 20

The lithium ion battery 100 includes the non-aqueous electrolytesolution 20. Normally, in a non-aqueous electrolyte solution lithium ionbattery, a non-aqueous electrolyte solution exists inside the cathode,inside the anode, and between the cathode and the anode, which securesthe lithium ion conductivity between the cathode and the anode.

The non-aqueous electrolyte solution 20 normally includes a lithiumsalt. Examples of the lithium salt include inorganic lithium salts suchas LiPF₆, LiBF₄, LiClO₄ and LiAsF₆, and organic lithium salts such asLiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ and LiC(CF₃SO₂)₃. For the lithiumsalt, one kind may be used alone, or a mixture of two or more kinds mayalso be used.

The non-aqueous electrolyte solution 20 normally includes a non-aqueoussolvent that dissolves the above-described lithium salts. Examples ofthe non-aqueous solvent include: cyclic esters (cyclic carbonates) suchas ethylene carbonate (EC), propylene carbonate (PC) and butylenecarbonate (BC); γ-butyrolactone; sulfolane; N-methyl pyrrolidone (NMP);chain esters (chain carbonates) such as 1,3-dimethyl-2-imidazolidinone(DMI); dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylmethylcarbonate (EMC); acetates such as methyl acetate and ethyl acetate; andethers such as 2-methyltetrahydrofuran. For the non-aqueous solvent, onekind may be used alone, or a mixture of two or more kinds may also beused.

The concentration of the lithium salt in the non-aqueous electrolytesolution 20 may be, for example, in the range of from 0.3 mol/L to 5.0mol/L, and may be in the range of from 0.8 mol/L to 1.5 mol/L. If theconcentration of the lithium salt is too low, the capacity in a highrate might lower. If the concentration of the lithium salt is too high,the viscosity becomes high and the capacity at a low temperature mightlower. As the non-aqueous electrolyte solution 20, for example a lowvolatile liquid such as ionic liquid may also be used.

1.3. Anode 30

The anode 30 may have the same structure as that of the anode of aconventional lithium ion battery. For example, the anode 30 includes aconductive material 31, an anode active material 32 and a binder 33. Inthe anode 30, the anode active material 32 is necessary, but theconductive material 31 and the binder 33 are optional. In the anode 30,an anode mixture layer 34 is formed from the anode active materials 32etc. The anode mixture layer 34 is connected to an anode currentcollector 35, which makes it possible to take out the electrical energyfrom the current collector, via terminals and the like (not shown). Theanode active material 32 is not particularly limited as long as it canocclude/release lithium ions. Examples thereof include active materialsformed from carbon materials, active materials formed from oxides andactive materials formed from metal. Examples of the carbon materialsinclude graphite, mesocarbon microbeads (MCMB), highly orientedpyrolytic graphite (HOPG), hard carbon and soft carbon. Examples of theoxides include Nb₂O₅, Li₄Ti₅O₁₂ and silica. Examples of the metalinclude Li, In, Al, Si, Sn and alloys thereof. The shape of the anodeactive material 32 may be in a particle form or thin film form forexample. If the anode active material 32 is formed in particles, theprimary particle diameter may be in the range of from 1 nm to 100 μm.The lower limit may be no less than 10 nm, may be no less than 100 nm,and may be no less than 500 nm. The upper limit may be no more than 30μm, and may be no more than 10 μm. The anode active material 32 may forma secondary particle in which the primary particles are gathered oragglomerated. In this case, the particle diameter of the secondaryparticle is not particularly limited, and normally in the range of from3 μm to 50 μm. The lower limit may be no less than 4 μm, and the upperlimit may be no more than 20 μm. The content of the anode activematerial 32 in the anode mixture layer 34 may be, for example, in therange of from 40 mass % to 99 mass %. The conductive material 31 and thebinder 33 may be adequately selected from the examples of the conductivematerial 11 a and the binder 13 of the cathode 10. The conductivematerial 31 and the conductive material 11 a may be formed fromdifferent materials. The materials of the binder 33 and the binder 13may also be different. The contents of the conductive material 31 andthe binder 33 in the anode mixture layer 34 are not particularlylimited. The anode current collector 35 is, for example, formed from ametal material including one or two or more elements selected from thegroup consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Geand In.

1.4. Separator 40

The lithium ion battery 100 may include a separator 40 between thecathode 10 and the anode 30. In the lithium ion battery 100, theseparator 40, the cathode 10 and the anode 30 are immersed in thenon-aqueous electrolyte solution 20. For the separator 40, any separatorused in a conventional non-aqueous electrolyte solution lithium ionbattery may be used. The separator 40 may be a porous film for example.The separator 40 may be formed from an organic material, or may beformed from an inorganic material. Specific examples of the separator 40include a single-layered organic porous film of polypropylene (PP) orpolyethylene (PE), and a PP/PE/PP layered type organic porous film. Thethickness of the separator 40 is not particularly limited, and it may bein the range of from 0.1 μm to 1000 μm, and may be in the range of from0.1 μm to 300 μm.

A power generation element is formed from the above-described cathode10, non-aqueous electrolyte solution 20 and anode 30, to be the lithiumion battery 100. In the lithium ion battery 100, the cathode 10 includesthe layered niobium-containing oxide 11 b that coats the surface of theconductive material 11 a. Thus, generation of gas due to decompositionof the non-aqueous electrolyte solution on the surface of the conductivematerial 11 a can be inhibited.

2. Method for Manufacturing Lithium Ion Battery 100

The lithium ion battery 100 may be manufactured by the method disclosedin FIG. 2, for example. The manufacturing method (S100) disclosed inFIG. 2 includes a first step (S1) of coating the surface of theconductive material 11 a with the layered niobium-containing oxide 11 bto form the complex 11, a second step (S2) of mixing the complex 11 andthe lithium-containing oxide active material 12 having an upperpotential to the redox potential of metal lithium of no less than 4.5 V(vs. Li/Li⁺) to obtain a cathode mixture, a third step (S3) ofmanufacturing the cathode 10 from the cathode mixture, and a fourth step(S4) of manufacturing a power generation element from the cathode 10,the non-aqueous electrolyte solution 20 and the anode 30.

2.1. First Step (S1)

In S1, the surface of the conductive material 11 a is coated with thelayered niobium-containing oxide 11 b to form the complex 11. S11 may becarried out by various methods. For example, a method of forming a filmof the niobium-containing oxide 11 on the surface of the conductivematerial 11 a by atomic layer deposition (ALD), chemical vapordeposition (CVD), sputtering, and a method of spraying a precursor ofthe niobium-containing oxide over the surface of the conductive material11 a and thereafter drying the film, and the like. Among them, ALD maybe used because the thickness of the layered niobium-containing oxide 11b can be easily controlled by increasing/decreasing the cycle number ofthe supply and purge of the precursor. With ALD, it is possible touniformly provide an extremely thin layer of the niobium-containingoxide 11 b of no more than 5 nm in thickness on the surface of theconductive material 11 a.

It is considered that a core is preferentially formed at the part offunctional group on the surface of the conductive material 11 a by ALD.For example, when the conductive material 11 a is formed from a carbonmaterial (e.g. acetylene black), it is considered that the formation andgrowth of the core is preferentially formed at the edge portion (endportion of graphene structure) dotted on the surface of the conductivematerial 11 a. Thus, it may be considered to be difficult to form auniform layer over the whole surface of the conductive material 11 a.Actually, when aluminum oxide is accumulated on the surface of acetyleneblack, the aluminum oxide is dotted on the surface of the acetyleneblack to form a layer having many gaps. However, as a result ofintensive research by the inventors of the present disclosure, when onlya niobium-containing oxide was used, it was surprisingly possible toform a uniform layer of less than 5 nm in thickness over the wholesurface of the niobium-containing oxide by ALD, even though the surfacehad the dotted edge portion like the carbon material (see FIG. 3).

2.2. Second Step (S2)

In S2, the complex 11 and the lithium-containing oxide active material12 having an upper potential to the redox potential of metal lithium ofno less than 4.5 V (vs. Li/Li⁺) are mixed to obtain a cathode mixture.The binder 13 may be mixed in addition to the complex 11 and the activematerial 12. A solvent may also be added to make the cathode mixturehave a slurry form. The mixing ratio of the complex 11, the activematerial 12 and the binder 13 is as mentioned above. S2 may be carriedout by various mixing methods. For example, as a mixing method, mixingmanually by means of a mortar, and mixing mechanically by a shaker,ultrasonic wave disperser, stirring machine, and the like may be used.If the mixing energy in S2 is too large, the complex 11 is crushed, andthe niobium-containing oxide 11 b peels off from the complex 11. Themixing method may be selected with consideration of energy to be addedto the complex 11.

2.3. Third Step (S3)

In S3, the cathode 10 is manufactured from a cathode mixture. When thecathode mixture is in a slurry form including a solvent, the cathode 10including a cathode mixture layer 14 on the surface of the cathodecurrent collector 15 may be easily manufactured by applying the slurryonto the surface of the cathode current collector 15, by a doctor bladeand the like, and drying the slurry. When the cathode mixture does notinclude a solvent, for example, when the cathode mixture is in a powderform, the cathode 10 including the cathode mixture layer 14 on thesurface of the cathode current collector 15 may be easily manufacturedby carrying out a press forming step on the powder and the cathodecurrent collector 15, while optionally heating them.

2.4. Fourth Step (S4)

In S4, a power generation element is manufactured from the cathode 10,the non-aqueous electrolyte solution 20 and the anode 30. For example,the cathode 10 and the anode 30 are accommodated in predeterminedpositions in a battery case. Here, a stack in which the separator 40 issandwiched by the cathode 10 and the anode 30 may be made, and the stackmay be accommodated in a predetermined position in the battery case.Then, the inside of the case is filled with the non-aqueous electrolytesolution 20 to immerse the cathode 10 and the anode 30 in thenon-aqueous electrolyte solution 20, whereby the power generationelement may be manufactured. After that, the battery case is sealed andso on, whereby the lithium ion battery 100 is obtained.

The manufacturing methods of the non-aqueous electrolyte solution 20 andthe anode 30 are the same as before. For example, the methods disclosedin Patent Literatures 1 to 5 may be referenced. Detailed explanation isomitted here.

EXAMPLES 1. Manufacture of Lithium Ion Battery

Lithium ion batteries according to Examples 1 to 7, Reference Example 1and Comparative Examples 1 to 3 were manufactured as follows.

Example 1 (Coating of Conductive Material)

A film of niobium oxide was formed on the surface of a conductivematerial (acetylene black, manufactured by Denka Company Limited,particle form, particle diameter: approximately 50 nm) by an ALDapparatus (manufactured by PICOSUN Oy), whereby a complex was obtained.Niobium ethoxide was used as a niobium source, and water was used as anoxygen source. When the film was formed, the temperature of niobiumethoxide was 200° C., the temperature of water was 20° C., and thetemperature of the reaction vessel was 200° C. An input of niobiumethoxide, a purge, an input of water, and purge were determined as 1cycle (film formation rate: 0.4 Å/cyc), and 10 cycles were carried out.The thickness of the layered niobium oxide of the complex wasapproximately 0.4 nm.

(Manufacture of Cathode Mixture)

With a mortar, the complex and a lithium-containing oxide activematerial (LiNi_(0.5)Mn_(1.5)O₄) were mixed. To the obtained mixture,polyvinylidene fluoride (PVdF) dissolved in n-methylpyrrolidone (NMP)and a binder (manufactured by KUREHA CORPORATION) were added. Theobtained material was mixed and dispersed by a mixer, whereby a cathodemixture slurry was manufactured. In the cathode mixture slurry, the massratio of the lithium-containing oxide active material, the complex, andthe binder was 85:10:5.

(Manufacture of Cathode)

The cathode mixture slurry was applied on the surface of a cathodecurrent collector (aluminum foil, thickness 15 μm) by a doctor blade,and dried at 80° C. in air to remove NMP. Thereafter, the obtainedmaterial was dried in a vacuum at 120° C. for 10 hours. After that, thecathode mixture layer and the cathode current collector were pressed tobond to each other by pressure, whereby a cathode was obtained. Thethickness of the cathode mixture layer was approximately 30 μm.

(Manufacture of Lithium Ion Battery)

The cathode, an anode (graphite), and a non-aqueous electrolyte solution(in which lithium hexafluorophosphate (LiPF₆) as lithium salt wasdissolved to be 1 mol/L in concentration in a mixture solvent of EC andEMS of 3:7 in volume ratio) were sealed in a laminate pack, whereby alithium ion battery was manufactured.

Examples 2 to 6

Complexes were manufactured in the same manner as in Example 1, exceptthat the number of the cycles in ALD was changed to 25 cyc., 50 cyc., 75cyc., 125 cyc. and 175 cyc. Cathode mixtures, cathodes and lithiumbatteries were manufactured in the same manner as in Example 1. InExamples 2 to 5, the thicknesses of the layered niobium oxides in thecomplexes were approximately: 1 nm; 2 nm; 3 nm; 5 nm; and 7 nm,respectively.

Example 7 (Coating of Conductive Material)

A film of lithium niobate was formed on the surface of a conductivematerial (acetylene black, manufactured by Denka Company Limited,particle form, particle diameter: approximately 50 nm) by an ALDapparatus (manufactured by PICOSUN Oy), whereby a complex was obtained.Niobium ethoxide was used as a niobium source, lithium tert-butoxide wasused as the lithium source, and water was used as an oxygen source. Whenthe film was formed, the temperature of niobium ethoxide was 200° C.,the temperature of lithium tert-butoxide was 140° C., the temperature ofwater was 20° C., and the temperature of the reaction vessel was 235° C.An input of niobium ethoxide, a purge, an input of lithiumtert-butoxide, a purge, an input of water, and a purge, were determinedas 1 cycle (film formation rate: 2 Å/cyc.), and 10 cycles were carriedout. The thickness of the layered lithium niobate of the complex wasapproximately 2 nm.

(Manufacture of Cathode Mixture, Cathode and Lithium Ion Battery)

A cathode mixture, a cathode and a lithium ion battery were manufacturedin the same manner as in Example 1, except that the complex was changed.

Reference Example 1

A cathode mixture, a cathode and a lithium ion battery were manufacturedin the same manner as in Example 2, except that the following compositeactive material was used as the lithium-containing oxide activematerial.

(Manufacture of Composite Active Material)

A film of niobium oxide was formed on the surface of alithium-containing oxide active material in the same conditions as inExample 2 (25 cyc.), whereby a composite active material was obtained.In the composite active material, the thickness of the layered niobiumoxide was approximately 1 nm.

Comparative Example 1

A cathode mixture, a cathode and a lithium ion battery were manufacturedin the same manner as in Example 1, except that the coating ofconductive material was not carried out.

Comparative Example 2 (Coating of Conductive Material)

A surface of a conductive material (acetylene black, manufactured byDenka Company Limited, particle form, particle diameter: approximately50 μm) was coated with aluminum oxide by an ALD apparatus (manufacturedby PICOSUN Oy), whereby a complex was obtained. Trimethylaluminum wasused as an aluminum source, and water was used as an oxygen source. Whenthe coating was carried out, the temperature of trimethylaluminum was20° C., the temperature of water was 20° C., and the temperature of thereaction vessel was 200° C. An input of trimethylaluminum, a purge, aninput of water, and a purge were determined as 1 cycle (film formationrate: 1 Å/cyc.), and 10 cycles were carried out.

(Manufacture of Cathode Mixture, Cathode and Lithium Ion Battery)

A cathode mixture, a cathode and a lithium ion battery were manufacturedin the same manner as in Example 1, except that the complex was changed.

Comparative Example 3

A complex was manufactured in the same manner as in Comparative Example2, except that the number of cycles in ALD was changed to 30 cyc. Acathode mixture, a cathode and a lithium ion battery were manufacturedin the same manner as in Comparative Example 2.

2. Evaluation of Lithium Ion Battery

Evaluations of the manufactured lithium ion batteries were made by thefollowing method.

<Observation of Surface Condition of Complex>

HAADF-STEM images of the complex used in Example 3 were obtained by ahigh-angle annular dark-field method by means of a scanning transmissionelectron microscope (HAADF-STEM method). The results are shown in FIGS.3A, 3B, 4A and 4B. FIGS. 3A and 3B include an image to observe a crosssection of the complex after being filled with resin. FIG. 3A and FIG.3B are both HAAD-F STEM images of the cross section of the complex usedin Example 3, whose observation areas are different. FIG. 4A is an imageto show the surface of the complex before being filled with resin. FIG.4B is for analysis of the number of elements existing in the range shownby the arrow in FIG. 4A. The left end of the horizontal axis of FIG. 4Bcorresponds to the base end of the arrow, and the right end of thehorizontal axis corresponds to the tip of the arrow. From FIG. 4B, theelement ratio existing on the “surface” of the complex can bedetermined.

In FIGS. 3A, 3B, 4A and 4B, heavy metal (Nb) was included at theportions shown in white. As is apparent from FIGS. 3A, 3B, 4A and 4B, itwas possible to uniformly form a film of layered niobium oxide onto thesurface of the conductive material by ALD, without aggregating theniobium oxide. As to the complexes of Examples 1, 2 and 4 to 7, andReference Example 1 as well, it was possible to form a film of layeredniobium oxide or layered lithium niobate onto the surface of theconductive material, without aggregating them.

<Charge-Discharge Test>

A process of separating (releasing) lithium ions from the cathode wasdetermined as “charge”, and a process of inserting (occluding) lithiumions to the cathode was determined as “discharge”. A charge-dischargetest was carried out with a charge-discharge testing machine (HJ-1001SMSA, manufactured by HOKUTO DENKO CORPORATION). Charge and dischargewere repeated in the range of from 3.5 V to 4.9 V, with the currentvalue set as ⅓ C and at the temperature of 25° C. The discharge capacityat the third cycle was determined as the initial capacity. After that,the SOC was adjusted to 60%, and discharge was carried out at 5 C ratefor 10 seconds. From the drop voltage difference at the discharge, thebattery resistance was calculated. The results are shown in Table 1below.

In addition, charge and discharge were carried out for 100 cycles in therange of from 3.5 V to 4.9 V at the current value of 2 C and at thetemperature of 60° C. From the amount of swell of the laminate pack, theamount of gas generated in the battery was estimated. The results areshown in Table 1 below.

TABLE 1 gas ALD thickness cell generation cycle of coating kind ofresistance amount number layer (nm) coating layer (Ω) (cm³) Comp. 0 0 —3.1 1.13 Ex. 1 Comp. 10 — aluminum oxide 3.0 0.90 Ex. 2 Comp. 30 —aluminum oxide 3.2 0.87 Ex. 3 Ex. 1 10   0.4 niobium oxide 3.1 0.66 Ex.2 25 1 niobium oxide 3.2 0.65 Ex. 3 50 2 niobium oxide 3.1 0.62 Ex. 4 753 niobium oxide 3.2 0.60 Ex. 5 125 5 niobium oxide 3.5 0.59 Ex. 6 175 7niobium oxide 4.5 0.59 Ex. 7 10 2 lithium niobate 3.2 0.57 Ref. 25 1niobium oxide 6.1 0.51 Ex. 1

As is apparent from the results shown in Table 1, as to the lithium ionbatteries of Examples 1 to 7 and Reference Example 1, it was possible toremarkably inhibit the generation of gas due to decomposition of thenon-aqueous electrolyte solution on the surface of the conductivematerial when the batteries were charged and discharged, compared to thelithium ion battery of Comparative Example 1. In addition, from Examples1 to 7, it was determined that the gas generation amount became smallbut the cell resistance became large, as the thickness of theniobium-containing layered oxide increased. Considering as a reason ofthe increase in the cell resistance was that the resistance of electronat the interface of the conductive material increased, whereby thesupply of electrons delayed, as a result, the supply of electrons fromthe conductive material became a bottleneck. That is, from the resultsof Examples 1 to 7, it was determined that it was possible to keep thecell resistance low and at the same time to inhibit the generation ofgas, by making the thickness of the layered niobium-containing oxide inthe range of from 0.4 nm to 5.0 nm. Meanwhile, from the result ofReference Example 1, it was determined that it was possible to furtherhold down the generation amount of gas by coating not only theconductive material but also the surface of the cathode active materialwith the layered niobium-containing oxide. However, it was alsodetermined that the cell resistance excessively increased when thesurface of the cathode active material was coated with the layeredniobium-containing oxide.

In addition, from Comparative Examples 1 to 3, it was determined that itwas possible to hold down the generation amount of gas even when thesurface of the conductive material was coated with aluminum oxide.However, when the surface was coated with aluminum oxide, the remarkableeffect was not obtained as in a case in which the surface was coatedwith the niobium-containing oxide.

As described above, it was found that it was possible to remarkablyinhibit the generation of gas due to decomposition of a non-aqueouselectrolyte solution generated when a high-potential active material wasused, by forming a lithium ion battery with a cathode including aconductive material, a layered niobium-containing oxide that coats asurface of the conductive material, and a lithium-containing oxideactive material having an upper electrical potential to the redoxpotential of metal lithium of no less than 4.5 V (vs. Li/Li⁺).

INDUSTRIAL APPLICABILITY

The lithium ion battery according to the present disclosure may be usedfor various power sources as a primary battery or a secondary battery.For example, it can be applied as a power source for vehicle mounting.

The examples disclose various embodiments that are not intended to limitthe scope of the disclosure. It will be understood that various changesand modification can be made without departing from the scope of thisdisclosure.

DESCRIPTION OF REFERENCE NUMERALS

-   100 lithium ion battery-   10 cathode-   14 cathode mixture layer-   11 complex-   11 a conductive material-   11 b layered niobium-containing oxide-   12 lithium-containing oxide active material-   13 binder-   15 cathode current collector-   20 non-aqueous electrolyte solution-   30 anode-   34 anode mixture layer-   31 conductive material-   32 anode active material-   33 binder-   35 cathode current collector-   40 separator

What is claimed is:
 1. A lithium ion battery comprising: a cathode; anon-aqueous electrolyte solution; and an anode, wherein the cathodeincludes a conductive material, a layered niobium-containing oxide thatcoats a surface of the conductive material, and a lithium-containingoxide active material having an upper-limit potential to a redoxpotential of metal lithium of no less than 4.5 V (vs. Li/Li⁺).
 2. Thelithium ion battery according to claim 1, wherein a thickness of thelayered niobium-containing oxide is no less than 0.4 nm.
 3. The lithiumion battery according to claim 2, wherein the thickness of the layeredniobium-containing oxide is in the range of from 0.4 nm to 5 nm.
 4. Thelithium ion battery according to claim 1, wherein the conductivematerial consists of a carbon material.
 5. The lithium ion batteryaccording to claim 1, wherein said niobium-containing oxide includesniobium oxide and lithium niobate.
 6. The lithium ion battery accordingto claim 1, wherein said lithium-containing oxide includes a lithiumnickel manganese composite oxide.
 7. The lithium ion battery accordingto claim 1, wherein said conductive material is in a particulate formhaving a particle diameter of 5 nm to 100 nm and an aspect ratio of lessthan
 2. 8. The lithium ion battery according to claim 1, wherein saidconductive material is in a fibrous form having a fiber diameter of 10nm to 1 μm and has an aspect ratio of no less than
 20. 9. A method formanufacturing a lithium ion battery comprising: coating a surface of aconductive material with a layered niobium-containing oxide to form acomplex; mixing the complex and a lithium-containing oxide activematerial having an upper-limit potential to a redox potential of metallithium of no less than 4.5 V (vs. Li/Li^(p)) to obtain a cathodemixture; manufacturing a cathode from the cathode mixture; andmanufacturing a power generation element from the cathode, a non-aqueouselectrolyte solution and an anode.
 10. The method according to claim 9,wherein the coating of the layered niobium-containing oxide is by anatomic layer deposition (ALD).
 11. The method according to claim 9,wherein said layered niobium-containing oxide has a thickness of in therange of no less than 0.4 nm.
 12. The method according to claim 9,wherein said layered niobium-containing oxide has a thickness in therange of 0.4 nm to 5 nm.
 13. The method according to claim 9, whereinthe conductive material consists of a carbon material.
 14. The methodaccording to claim 9, wherein said niobium-containing oxide includesniobium oxide and lithium niobate.
 15. The method accordingly to claim9, wherein said lithium-containing oxide includes a lithium nickelmanganese composite oxide.
 16. The method according to claim 9, whereinsaid conductive material is in a particulate form having a particlediameter of 5 nm to 100 nm and an aspect ratio of less than
 2. 17. Themethod according to claim 9, wherein said conductive material is in afibrous form having a fiber diameter of 10 nm to 1 μm and has an aspectratio of no less than 20.